Railway axleboxes include bearing housings configured to directly or indirectly mount roller bearings supporting the axles of the railway vehicle. In the so-called two-part design, the housing has a split design with an upper and a lower part each having a semi-circular bearing seat surface encompassing the radially outer surface of the baring, which is then the mounting surface of the bearing assembly.
In the so-called three-part design, the bearing is fitted into an outer sleeve, which is then held in the housing and which provides the radially outer mounting surface.
In both cases, the risk of fretting corrosion at the interface between the radially outer mounting surface and the inner surface of the housing his high. This risk is increased by current returns between the surfaces. Further the problem of inaccurate location of the bearing load is likely to arise if the machining of either the mounting surface of the inner surface of the housing happens to be imprecise. Initial imprecisions or fretting corrosion may further lead to radial or axial play and cause wear.